The invention relates to an interference suppressed universal motor, preferably for electrical hand tool machines.
Electrical hand tool machines require compact high-performance universal motors for driving the tool. The power supply in mains-supplied electrical hand tool machines is provided via a power cable. A commutator swivel switch with a rotationally pivotable brush mounting plate is provided for switching the rotational direction of the universal motor.
An interference suppressing capacitor is usually used on the power cable side for suppressing transfer to the power cable of higher-frequency brush sparking occurring at the carbon brushes. The interference suppressing capacitor forms a low-pass with a brush-side field coil for each power line.
According to U.S. Pat. No. 6,037,693, an interference suppressed universal motor has an interference suppressing capacitor on the power cable side, which forms a low-pass with a brush-side field coil on each power line. The symmetrical arrangement of the two field coils on each of the two carbon brushes is disadvantageous in compact universal motors for electrical hand tool machines.
According to EP 9 248 48 A2, a thyristor controlled universal motor of a mains powered electrical hand tool machine has two directly series-connected field coils. In motor operation, a carbon brush is connected directly with a power line, whereby high-frequency interference signals can propagate undamped over the power cable.